Demography of the kittiwake in the Iroise Sea

SEDERISSA: Iroise sea kittiwake demographic series

This demographic series is part of the Observatoire Marin of the IUEM: Institut Universitaire Européen de la Mer
This study based on individually marked birds focusses on the kittiwake (Rissa tridactyla), a long-lived seabird species. Kittiwakes have been marked using plastic color bands since year 1979 in colonies located in Cap Sizun. More than 19 000 birds have been marked, mostly as chicks.
This demographic study has two main goals:
1/ Habitat selection, dispersal and population dynamics. This part of the project aims at estimating movement probability among colonies and sub-colonies, at understanding how individuals choose their breeding habitat and how this influences the number and identity of pairs breeding in the different locations. Specifically, the factors influencing an individual’s decision to leave a breeding site, and to select a new site, are of special interest. This may include individual characteristics (age, experience, sex, etc.) or environmental factors (e.g., social context, the presence of predators destroying kittiwake eggs for example). Historically, 6 colonies located on the mainland and several other colonies located on islands in the Iroise sea have been monitored, with different field effort. Birds have been marked in all the mainland colonies, but not in all the years of the study.
2/ Life histories. Longitudinal data show that there is substantial variation among individual lifetime trajectories (age of first reproduction, longevity, series of reproductive states – successful or failed reproduction, nonbreeding) and total breeding success (the total number of offspring produced by an individual). This part of the project aims at understanding factors influencing an individual’s lifetime trajectory: the conditions experienced during growth, before recruitment, other factors such as the presence of predators in colonies, extreme climatic events, and the decisions of the individual itself in terms of breeding site selection and mate, etc.
Data from marked individuals
In this context, several data types from marked individuals are collected every year:
Resightings: has the individual been resighted in a given year?
Individual state: only in individuals that have been resighted in a given year
Definition of yearly individual ‘state’:
Breeder/nonbreeder: the criterion to classify an individual as a ‘breeder’ is the construction of a complete nest. A nonbreeder is necessarily resighted (a bird not observed in a given year does not have a state in that year).
In breeders only:
Number of eggs laid
Failed breeder/successful breeder. A successful breeder is an individual that raised at least one chick to independence (the chick was able to fly and to return to the nest to be fed by the parents).
Number of chicks raised to independence
Unknown: observers have not been able to assess state in a given year.
Location: only in individuals that established in a specific location. This includes breeders and nonbreeders.
Nest site state
Data from nest sites are also collected regardless of whether they are occupied by marked individuals
Nest site construction
Clutch size
Breeding success
Number of chicks raised to independence
Subjectivity. Each of these states is assessed by data producers on the basis of several observations from the individual each year: states are interpreted data and are subjective.
For example, location is usually straightforward to assess in breeders, but not in nonbreeders: in the latter observers assign a specific location based on the frequency and proportion of resightings in the location compared to other locations. The location assigned to a nonbreeder can be a nest site, a sub-colony or a colony. Similarly, the ‘nest completion’ criterion is assessed by observers: an individual is considered as a breeder depending on the interpretation of the observed state of the nest by the observer.
Precision. There is a degree of precision associated with individual yearly states. For example, the number of eggs laid cannot always be assessed, especially when predators destroy eggs very quickly after egg laying. Observers may see a chick flying but not return to its nest. They may also see the chick on its nest when 35 days old (theoretically, the chick is able to fly), but not see the chick flying. Sometimes the fate of a chick from a brood can be assessed, but not the fate of all the chicks.
It is important to note that states have not been assessed in all the locations in all years in a consistent manner. In particular, the field effort in islands has consistently been lower than on the mainland.
Some individual longitudinal trajectories may contain yearly states with different levels of accuracy. If entire longitudinal trajectories with a consistent level of accuracy are required, this may considerably decrease sample size.
Database dynamics
This is an ongoing project and data change regularly. For example, birds are sexed through behavior and when the sex of an individual is determined, its current and former mates can also be sexed retrospectively. For this reason, data extracted from the database provide an instantaneous ‘picture’ of the knowledge of data producers and database managers available at the time the data are extracted. Similarly, information from recoveries is regularly updated by the Centre de Recherche sur la Biologie des Populations d’Oiseaux (Museum National d’Histoire Naturelle, Paris). Data extracted at different points in time will not necessarily lead to the same dataset even if identical request parameters are used.
This study was started by Jean-Yves Monnat (Université de Bretagne Occidentale, France) in year 1979. Emmanuelle Cam is currently in charge of the project (Université Toulouse III, France). Jean-Yves Monnat and Emmanuelle Cam are the main data producers and database creators and managers. More than 150 collaborators have been or are still involved in data collection: their contribution is invaluable. The data producers represent the work of all the colleagues, volunteers, friends and girlfriends who have contributed to this project.
Contact: Emmanuelle Cam (
Data collection: Cap Sizun (Finistère, France)

This research program  is  authorized  by  the  Centre  de  Recherches  sur  la  Biologie  des  Populations  d’Oiseaux
(CRBPO, Museum d’Histoire Naturelle, Paris, France). The permit to capture kittiwakes and mark them was granted by the CRBPO. All work is carried out in accordance with standard animal care protocols approved by the CRBPO.